The objective of the project is to define more fully the nature of the reactants present in soluble antigen-antibody complexes in rheumatoid arthritis and related connective tissue diseases. With respect to rheumatoid arthritis we propose to: a) dissociate synovial fluid complexes, b) determine the specificity of the dissociated antibody which is reactive with single-stranded calf thymus DNA, c) characterize the DNA present in soluble complexes in rheumatoid synovial fluid with respect to buoyant density in cesium chloride, and melting temperature, d) evaluate the role of rheumatoid factor in modifying complement fixation by this complex, e) determine the frequency of antigen-antibody complexes in the serum of patients with rheumatoid arthritis and related connective tissue diseases.